1. Field of the Invention
The present invention relates to shroud supports for use in gas turbine engines and more particularly relates to a shroud support having an aft end region which is equipped with two rails which function as an air-tight seal. The two rails define a gap which is located above an aft region of a shroud. The two rails prevent cooling air from escaping to the aft of the shroud support thereby reducing the amount of cooling air needed to cool the shroud. Since the present invention reduces the need for cooling air, more air can be utilized to enhance engine performance.
2. Discussion of the Background
FIG. 1 is an exemplary schematic illustration of the first stage of a two-stage high pressure turbine located in a gas turbine engine. Very hot gas, identified as gas flow 4, exits the combustor 6 and flows through vane 8 and rotor or turbine blade 10 in the initial turbine stage. The rotor blades of the turbine, such as rotor blade 10, convert energy contained in the gas flow 4 into mechanical energy which drives the upstream high pressure compressor (not shown).
With further reference to FIG. 1, located radially outward from the combustor 6 is cooling air flow 12 which originates from the high pressure compressor. Holes in the support arm 14 allow the cooling air 12 to continue to flow in at aft direction toward the shroud 16 and shroud support 18. The shroud support is connected to an outer casing 20 by means of hooked connections. The shroud support 18, as its name implies, is connected to and supports the shroud 16. Shroud support 18 forms a plenum from which cooling air 12 is directed onto shroud 16. A plurality of shrouds and shroud supports extend circumferentially around the turbine stage of the gas turbine engine with two shrouds being supported by each shroud support. Rotor blades are located radially inward of the shrouds.
The shrouds are secured above the rotor blades so as to provide tight radial clearance for efficient engine operation. Thus, shroud 16 is located very close to the working medium gas flow (i.e., hot gas flow 4). In fact, the radially inward side of the shroud is exposed to temperatures which can actually exceed the melting point of the metal from which the shroud is made. However, the shroud does not melt as a result of the cooling air flow 12 which is directed along its radially outward side.
Thus, it is important that the shroud support remain relatively cool as compared to the shroud to which it is connected. Furthermore, to reduce heat conduction from the shroud, the amount of surface area contact between the shroud and shroud support has typically been minimized. Existing designs have reduced conduction by spacing pads circumferentially around the shroud support surface. Such a design effectively reduces the contact area between the shroud support and the shroud, but it does not prevent leakage flow of cooling air from escaping between pads to the aft of the shroud support. Such leakage results in significant amounts of cooling air being wasted.
Thus, a need exists for a shroud support which is provided with a means for reducing heat conduction and which significantly reduces or eliminates the leakage of cooling air.